In the Unites States chronic wounds affect the nation's population and health care costs. It has been estimated that more than six million people suffer from chronic wounds, deriving from decubitus, vascular, inflammatory, and rheumatologic sources. The number of such people is expected to increase due to the growth in the elderly population and the prevalence of diabetes in such population. Concurrently, the growing population with chronic wounds leads to an increase in medical costs as evidenced by a study showing that chronic wound care cost $9.7 billion in 2004. Therefore, an improvement of chronic wound treatment in medical procedures would address a number of social and medical issues.
One of the problems accompanying chronic wound treatment is associated with pain that a patient may suffer. It has been found that up to 69% of patients with chronic venous ulcers suffer significant pain. Pain may be even more severe for patients suffering from an underlying disease process such as diabetic peripheral neuropathy.
For appropriate pain management in patients with chronic wounds, it is necessary to determine the source of the pain, i.e., whether the pain arises from the wound itself or from the underlying disease. If the pain is due to the wound itself, treatment of the wound with moisture retentive wound dressings, controlling infection, assuring adequate circulation, and reducing edema are a typical protocol to relieve the pain. If the pain is associated with an underlying disease such as diabetes mellitus, successful pain management requires special care as well as primary care since pain is often worsened by wound treatments, such as dressing changes as well as vulnerable periwound skin. In fact, one study showed that it was a major concern for 43% of medical practitioners to control acute pain during wound debridement. Another study confirmed that wound treatments themselves such as dressing removal, debridement, and inappropriate dressing selection promote wound related pain. Therefore, it is necessary to use analgesics or anesthetics during wound treatments.
Analgesics are categorized into two types, narcotics and non-narcotics, and are frequently used for long-term pain relief in patients with chronic wounds. However, the long-term use of either narcotics or non-narcotic can lead to tolerance and necessity of dose escalation. The former leads to addiction, dependence and tolerance while the latter causes a ceiling effect.
Topical anesthetics are widely used to numb the skin and to relive pain in medical and surgical procedures in anesthesia, ophthalmology, otorhinolaryngology, dentistry, urology, and aesthetic surgery. Among topical anesthetics, lidocaine, tetracaine, benzocaine, and prilocaine in a cream, ointment, or gel are commonly available prescription and/or over-the-counter (OTC) topical anesthetics.
Of the anesthetics, both lidocaine and benzocaine are most popular and commonly used in medical procedures. Lidocaine absorbs more quickly where applied due to its higher water-solubility and tends to last longer than benzocaine. Thus, benzocaine is often found in sunburn and oral ulcer products whereas lidocaine is more often found in prescription medications. Unfortunately, lidocaine is most effectively absorbed through mucosal surfaces, not skin.
Lidocaine HCl has been used in topical dosage forms for topical anesthesia in mucosal tissues and could be attractive, particularly if it is used as a topical anesthetic in non-mucosal tissues to reduce the debridement pain arising from chronic open wounds.
For example, compositions and methods for treating a disease, such as infection, pain or inflammation are reported in PCT International Publication No. WO 2011/153334 to Trilogic Pharma LLC. The composition comprises water, polyethylene glycol and/or ethyl alcohol, poloxamer, xanthan gum and active ingredients. Among various active ingredients, benzocaine is preferably used since it provides a superior degree of pain relief or analgesia for an extended period of time. The composition is implanted into a bodily cavity or applied to a tissue or oral mucosa.
Compositions and methods for delivering a drug for preventing bacterial infections are reported in PCT International Publication No. WO 2009/073658 to Trilogic Pharma LLC. The composition comprises water, copolymer, xanthan gum and an antibiotic, an anesthetic, or an analgesic. The composition is implanted into open cavities of human tissue including periodontal pockets, surgical incisions and open wounds.
Compositions and methods for preparing a local anesthetic in base form in order to obtain topical anesthesia through skin are reported in U.S. Pat. No. 4,529,601 to Astra Lakemedel Aktiebolag and U.S. Pat. No. 4,562,060 to Astra Lakemedel Aktiebolag (EMLA® cream). The composition comprises a mixture of lidocaine and prilocaine in the form of its base in a weight ratio of 1:1 (2.5% and 2.5%) with purified water (92%), which delivers the topical anesthetic through the skin. However, it takes at least 60 minutes for the anesthetic to take effect and an occlusive dressing after an application of the cream is necessary.
Fast acting compositions of topical transdermal anesthetics are reported in U.S. Pat. No. 5,993,836 to Castillo. The composition comprises a eutectic mixture of lidocaine and prilocaine in a weight ratio of about 3:1 in a lipophilic base. The composition takes effect in as little as 10-40 minutes without occlusive dressing for incision, excision, ablation, vaporization and coagulation of body soft tissues in medical specialties including aesthetic (dermatology and plastic surgery), podiatry, otolaryngology (ENT), gynecology, neurosurgery, arthroscopy (knee surgery) and invasive and endoscopic general surgery. The average desensitization period of the composition is 180 minutes.
Despite these existing treatments as indicated above there remains a need for topical anesthetics, particularly for use in chronic open wounds to reduce the debridement pain. Accordingly, it is an object of the present invention to provide a topical anesthetic which reduces the debridement pain. Another object of the present invention is to provide a topical anesthetic which exhibits a consistent anesthetic effect with no significant patient to patient variability. Yet another object of the present invention is to provide a topical anesthetic which has a predictable duration of anesthetic effect.